1. Field of the Invention
The present invention relates, generally, to pistons for internal combustion engines and, more specifically, to a piston and connecting rod assembly having improved coolant flow capabilities.
2. Description of the Related Art
Internal combustion engines known in the related art may generally include, among other basic components, an engine block having one or more cylinders, cylinder heads associated with the engine block and pistons supported for reciprocal movement in each cylinder. The piston generally includes a body having a crown and a skirt that depends from the crown. A connecting rod operatively interconnects the piston with a crankshaft. A pin bore is formed in the body and corresponds to a similar bore in the connecting rod. A pin is placed through the corresponding bores to attach the piston to the connecting rod.
Generally, fuel is combusted within the cylinders to reciprocate the pistons. The pistons drive the connecting rod, which drives the crankshaft, causing it to rotate within the engine block. In this way, power may be translated from the crankshaft to drive an automotive vehicle or any number of other devices. Specifically, the combustion pressure within the cylinder drives the piston downward in a substantially rectilinear motion.
The upper surface of the piston crown defines the floor of the combustion chamber within a cylinder. Specifically, the piston crown includes a recessed area commonly referred to as the “combustion bowl,” which receives the brunt of energy that is released when fuel is combusted during the operation of an internal combustion engine. Thus, the piston crown is subjected to a disproportionate amount of thermal and mechanical load relative to the remaining portion of the piston body.
In view of these relatively harsh conditions, it is known to provide cooling galleries formed along the underside of the piston crown that are used to reduce surface temperatures on the piston. Generally, the cooling galleries are voids formed within the piston body that are adapted to receive oil as the piston cycles within the cylinder. Movement of the piston within the cylinder transfers oil throughout the cooling galleries, thereby creating a “cocktail shaker” effect as the oil splashes against the walls of these galleries. In this way, the surrounding area of the piston is cooled.
Pistons of the type generally known in the related art may include inner cooling galleries that are generally formed in the body of the piston beneath the crown; and outer cooling galleries that are formed radially spaced from the inner cooling gallery and located closer to the exterior wall of the piston between the skirt and the body of the piston. A wall usually extending between the skirt and the body defines the bottom of the outer cooling gallery. Typically, the inner cooling gallery is longitudinally spaced from the outer cooling gallery and located relatively beneath the outer cooling gallery. Often passages are formed between the inner and outer cooling galleries to promote flow of coolant therebetween.
However, because of the relative position of the inner and outer cooling galleries with respect to each other and the location of the wall that defines the bottom of the outer cooling gallery, the passages extending between the inner and outer cooling gallery are typically drilled through the body of the piston at an oblique angle relative to the surface of the inner cooling gallery. Often, they must be drilled from the interior of the inner cooling gallery outward toward the outer cooling gallery. The oblique passages are difficult to form in practice because they require special drills, equipment and procedures to ensure that a proper passage is effectively drilled in the body of the piston. Importantly, these special considerations increase the cost to manufacture the piston. In addition, and because of the difficulty involved in forming the oblique passages, the scrap rate of the piston can be higher than for those without passages formed between inner and outer cooling galleries. Accordingly, there remains a need in the related art for a piston that employs inner and outer cooling galleries but that may be manufactured with internal passages at a lower cost. In addition, there remains a need in the art for a piston and connecting rod assembly that promote efficient cooling of the related components of the assembly.